How to create a for loop in R for this peculiar calculation

Question

I can\'t figure out with this (apparently) simply kind of operation:

Given these two diferent dataframes df(A) (nrow=10,ncol=3) and df(B) (nrow

Answer 1

As an alternative to user164385's answer, which is very good, you can also use the following loop that will do the trick (even though they're not always optimal, loops can make it easier when beginning with R). Note that with all-numeric data, you can use matrices instead of dataframes:

A <- matrix(c(1,2,4,3,5,7,5,7,6,6,9,
              5.9,9,11,8,4.5,5.5,7.9,
              21,6.7,13.6,3.5,5,6,6,
              7.9,1,67,4,2), ncol=3, byrow=T)
B <- matrix(c(1,4,5,2,7,7,3,9,8), ncol=3, byrow=T)

results <- matrix(nrow=8, ncol=3)
for(i in 1:(nrow(A)-2)) {
  results[i,] <- colSums(A[i:(i+2),] * B)
}
results
      [,1]  [,2]  [,3]
[1,]  22.0 106.0 117.0
[2,]  31.0 150.0 124.2
[3,]  44.0 190.0 135.3
[4,]  37.5 162.5 148.7
[5,]  81.0 142.8 204.1
[6,]  57.0 113.9 182.7
[7,]  46.0 132.9 118.0
[8,] 216.5 111.3  53.0